The present invention relates to the structure of a serial printer, which supplies a fresh ink ribbon as the printer head travels along the platen of the printer, in particular, relates to such a serial printer which utilizes a mosaic printer head.
A mosaic printer head generates a character pattern with a plurality of dots selectively printed on a paper, and those dots are printed either by a thermal printer head which prints by changing the color of a treated thermal paper by heating a small area on that paper, or a needle type printer head which prints dots by striking an untreated paper with a printing needle through an ink ribbon. The example of the latter needle type printer head is shown in U.S. Pat. No. 3,896,918. Alternatively, the present applicant filed the improvement of a needle type printer head in U.S. Pat. No. 147,106 and West Germany patent application P 30 17 903.4.
In a serial printer utilizing a mosaic printer head, a printer head and a printing paper are positioned very close to each other, and an ink ribbon must be threaded in that narrow slit between paper and printer head as shown in FIG. 1, in which the reference numeral 1 is an ink ribbon, 5 is a platen, 6 is a printer head, 8 is a ribbon protector which is essentially a U-shaped thin plate provided to prevent marking an undesirable portion of a paper with an ink ribbon, and 13 is a paper. The printer head 6 has a plurality of printing needles which are selectively actuated and strike a paper through a window between a pair of arms of said U-shaped ribbon protector 8 and the ink ribbon 13 to print a desired pattern.
In such a needle type serial printer, when an ink ribbon is mounted, that ink ribbon must be threaded through the narrow slit between a ribbon protector and a printer head, and a one-way feed mechanism (not shown in FIG. 1) which feeds an ink ribbon in the predetermined direction, and further the path of an ink ribbon is not straight but is folded or curved. Therefore, it takes long time to manually mount an ink ribbon through those paths and involves much trouble, further, there is a disadvantage in that the operator's fingers become dirty when threading the ink ribbon.
Alternatively, the printer head 6 can be temporarily removed from the platen to provide a wide area between the printer head and the platen to thread the ink ribbon. However, the means for removing a printer head is rather complicated, and is not suitable for a small and simple serial printer.